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PCI Power Management Registers — Intel
®
82575EB Gigabit Ethernet Controller
324632-003 Intel
®
82575EB Gigabit Ethernet Controller
Revision: 2.1 Software Developer’s Manual and EEPROM Guide
January 2011 199
In contrast to the MSI capability structure, which directly contains all of the control/status information
for the function's vectors, the MSI-X capability structure instead points to an MSI-X Table structure and
a MSI-X Pending Bit Array (PBA) structure, each residing in Memory Space.
Each structure is mapped by a Base Address register (BAR) belonging to the function, located beginning
at 10h in Configuration Space. A BAR Indicator register (BIR) indicates which BAR, and a QWORD-
aligned Offset indicates where the structure begins relative to the base address associated with the
BAR. The BAR is permitted to be either 32-bit or 64-bit, but must map Memory Space. A function is
permitted to map both structures with the same BAR, or to map each structure with a different BAR.
The MSI-X Table structure typically contains multiple entries, each consisting of several fields: Message
Address, Message Upper Address, Message Data, and Vector Control. Each entry is capable of
specifying a unique vector.
The Pending Bit Array (PBA) structure contains the function's Pending Bits, one per Table entry,
organized as a packed array of bits within QWORDs.
The last QWORD is not necessarily be fully populated.
Note: The following color notation is used for reference:
Capability ID: 1 Byte, Offset 60h, (RO)
This field equals 11h indicating the linked list item as being the MSI-X registers.
Next Pointer: 1 Byte, Offset 61h, (RO)
This field provides an offset to the next capability item in the capability list. Its value of A0h points to
the PCIe* capability structure.
Message Control: 2 Byte, Offset 62h, (R/W)
The register fields are described in the table that follows. There is a dedicated register per PCI function
to enable separately their MSI.
Table 68. MSI-X Capability Structure
Byte
Offset
Byte 3 Byte 2 Byte 1 Byte 0
60h Message Control (0009h)
Next Pointer (0Ah) Capability ID (11h)
64h
1
1. Hardwired to 3h.
Table Offset Table BIR
68h
2
2. Hardwired to 2003h.
PBA Offset PBA BIR
Fields identical to all functions.
Read only fields.
Hard coded fields and strapping options.